I think you are being unreasonable but let me explain my point of view; (I know this is going to cause a reaction with some, but I emphasise, these are my opinion and I was asked
When our family go on holiday, we leave the house keys with my neighbour. I fully expect them to bring their family and to snoop around the house, and this year was no exception. For some people, the temptation is simply too much.
On returning to our house we found:
-leftover turd in the toilet. What the neighbour had not realised is that we turn off the mains when we are on holiday. So the inevitable happened and the toilet did not flush. Of course the outside tap did not work either, so they ended up having to use the water from the waterbutt, which was murky and hence the result in the toilet.
-We are a non smoking household and have an extremely sensitive mains powered fire alarm. So when they invited their smoking friends along and set of the fire alarm, they were somewhat horrified to discover that it did not "shut up" when the batteries were removed. This led to an amusing chain of events, that for space consideration, I can't write here.
-They were suppose to look after our tropical fish, but some died. I know this because the pet shop owner told me. My neighbour had gone in to get some replacements fish and had told the pet shop owner, presumably without realising it would get back to me!
There are some other examples, but again, for space consideration I can't write here. I paid my neighbours £20 for 2 weeks but even so, I believe that once you leave your house keys with someone else, you should not be too surprised if they treat your home like their own.
Nevertheless, my neighbour's family presence in my home for those 2 weeks protected our home, as word got round that the place was lived in and occupied. For that reason, whatever their mischief, it was worth it!